wanderson

I have been trying to diagnose a problem with a breadboard SD connector and noticed the following peculiar behavior when I use a 4gb microSD card in a Sparkfun microSD shield connected to a UNO. Notice that I have purposely set the ChipSelect pin to pin 1, even though the Sparkfun needs it to be pin 8... In fact I have changed the Chip Select to every pin between 1,3-10 and all seem to work. When I run this sketch I get a summary of the card, followed by a list (correct list) of files on the card...

This example shows how use the utility libraries on which the' SD library is based in order to get info about your SD card. Very useful for testing a card when you're not sure whether its working or not. The circuit: * SD card attached to SPI bus as follows: ** MOSI - pin 11 on Arduino Uno/Duemilanove/Diecimila ** MISO - pin 12 on Arduino Uno/Duemilanove/Diecimila ** CLK - pin 13 on Arduino Uno/Duemilanove/Diecimila ** CS - depends on your SD card shield or module. Pin 4 used here for consistency with other Arduino examples

void setup(){ // Open serial communications and wait for port to open: Serial.begin(9600);

Serial.print("\nInitializing SD card..."); // On the Ethernet Shield, CS is pin 4. It's set as an output by default. // Note that even if it's not used as the CS pin, the hardware SS pin // (10 on most Arduino boards, 53 on the Mega) must be left as an output // or the SD library functions will not work. pinMode(10, OUTPUT); // change this to 53 on a mega pinMode(chipSelect, OUTPUT);

// we'll use the initialization code from the utility libraries // since we're just testing if the card is working! if (!card.init(SPI_HALF_SPEED, chipSelect)) { Serial.println("initialization failed. Things to check:"); Serial.println("* is a card is inserted?"); Serial.println("* Is your wiring correct?"); Serial.println("* did you change the chipSelect pin to match your shield or module?"); return; } else { Serial.println("Wiring is correct and a card is present."); }

// Now we will try to open the 'volume'/'partition' - it should be FAT16 or FAT32 if (!volume.init(card)) { Serial.println("Could not find FAT16/FAT32 partition.\nMake sure you've formatted the card"); return; }

// print the type and size of the first FAT-type volume uint32_t volumesize; Serial.print("\nVolume type is FAT"); Serial.println(volume.fatType(), DEC); Serial.println();

The Sparkfun card has a hex buffer as a 5V to 3.3V level converter. If the buffer input pin, pin 8, is not initialized this buffer often pulls CS on the SD card low. The SD will appear to ignore CS but will likely be flaky since noise may cause pin 8 to go high and disable the SD.